Re-take - Useful Information for 2394 :

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4 hours Ago # 763 ◄ Look at connector block's drawings Step 2 & Step 3 ..

Take your inspiration from GN-3 P/37 Drawing . Continuity of ring final circuit conductor Exam

 

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BS-7671: have stated the facts .

R. P/34 , Residual current operated circuit breaker with integral overcurrent protection ( RCBO ) A residual current operated switching device designed to perform the functions of protection against overload & / or short-circuit .

RCBOs provide both earth-fault & overcurrent-protection

30mA BS-EN-61009-1 provides :
independent RCD protection to individual circuits offering both the degree of additional protection that may be required by Regulation 415.1 and the minimum of inconvenience following a single-earth-fault ( Regulation 314.1 ).

R. P/26 , Earth-fault current . A current resulting from a fault of negligible impedance between a line conductor and an exposed-conductive-part or a protective-conductor .

R. P/34 , Short-circuit current . An overcurrent resulting from a fault of negligible impedance between ( live-conductors ) refer .

 

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Measurement of the résistance ( R[SUP]A[/SUP] )
( 50 ) is the maximum safety touch voltage limit :

TT - system .
protected by a RCD the maximum ( R[SUP]A[/SUP] ) values are :

BS-EN-61009-1 .. Uo /230V
BS-EN-61008-1 .. Uo /230V

( Ia ) is the rated residual operating current ( I∆n )
Table 41.5 . Rated residual operating current ( I∆n ) 30 , 100 , 300 , 500 . ( mA )

( R[SUP]A[/SUP] ) with touch voltage of 50V : 1667* , 500* , 167 , 100 . ( Ω )

Verification of the protection by RCD in a TT - system

411.5.3. Where an RCD is used for fault protection , the following conditions shall be fulfilled :
( R[SUP]A[/SUP] ) x I∆n ≤ 50V .

where :
R[SUP]A[/SUP] ) is the sum of the résistances of the earth electrode and the protective conductor connecting it to the exposed-conductive-parts . ( Ω )
I∆n ) is the rated residual operating current of the RCD

The requirements of the regulation are met if the earth fault loop impedance of the circuit protected by the RCD meets the requirements of Table 41.5.

Note 2 : Where ( R[SUP]A[/SUP] ) is not known , it may be replaced by ( Zs )
BS-7671:2011: shall be verified by ; ( R[SUP]A[/SUP] ) or ( Zs ) table 41.5. 50V ÷ 30mA = 1.666666667Ω .. 1667* maximum ( Zs ) earth fault loop impedance
Loop tester ( Ω ) example .
Maximum permissible value is 1667Ω ( RCD = 30mA and contact voltage limit of 50V ) instrument reads 12.74Ω , thus the condition ( R[SUP]A[/SUP] ≤ 50/Ia is respected )

R/P.57 . recap : Note 2 . * The résistance of the installation earth electrode should be as low as practicable . A value exceeding 200Ω may not be stable . refer

RCD is essential for protection , must be tested .

 

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R/P.55 . ► recap . The values specified in Table 41.3. for the types & ratings of overcurrent devices listed may be used instead of calculation .

Something I knocked up . ( Zs ) you're Q . Maximum

BS-EN-61557-3

GN-3 ; P/83. Earth fault loop impedance tester , These instruments may also offer additional facilities for deriving prospective fault current
( MT ) Earth fault loop impedance tester . also have the ( PFC ) measurement .

TN- system , example of ( Verification of the protection by Circuit-breaker ) BS-EN-60898-1

Characteristic circuit-breaker ( C ) Table 41.3 16A - Zs - 1.44Ω
Maximum value : of ( Zs ) is 1.44Ω .. the instrument reads 1.14Ω or 202A on Fault current range , it means that the Condition ( Zs x Ia ≤ 1.14Ω )
is respected .

in fact the ( Zs ) of 1.14Ω is less than 1.44Ω .. or the Fault current of 202A is more than ( Ia of 160A )

Fault between Line & Earth , the wall socket-outlet tested , The circuit-breaker will trip within the disconnection time required . ( Protected )

R/P.302 . Fig 3A5 . Type C . Rating 16A - Current 160A ; 16 - 160A

 

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Something I knocked up , Rotation instruments . GN-3 P/84 . 612.12. Check of phase sequence . refer

recap : GN-3 measuring equipment for testing the phase sequence in three-phase distribution system whether indication is given by ;
- mechanical .
- Visual .
- & or audible means .

MEM 100A three-phase distribution board

MFT : Megger - 1730 . Phase rotation / sequence test .

Three phase installation you measure or check that you have your Phase sequence correct right through the whole of the installation . Origin of supply then need be every Distribution boards .

turn onto phase sequence
( V ~ rotation Hz ) 50.0 Hz .. L1 , L2 , L3 . run in that sequence .

L1 - 426V , L2 - 426V, L3 - 426V Indicators , Visual .. ( V ~ )
3 alligator clips ; U1 / red , V1 / blue , W1 / green .

Example only . reversal on leads not red , blue , green . ( demonstrate purposes only )
U1 / blue , V1 / red , W1 / green .. L1 - 426V , L3 - 426V , L2 - 426V . flashing that indicates that there is something wrong

( demonstrate purposes only )
GN-3 P/84 . measuring equipment for testing the phase sequence in three-phase distribution systems whether indication is given by

Approved voltage Indicator . ( Visual means )

Fully compliant with GS-38

Voltage & Continuity Testers with Phase Rotation Test
CombiVolt 1 Voltage/Continuity Tester

Depicts a test carried out . Three phase installation .
Voltage indicators . ( L1 ) is black lead & ( + L2 ) in the black & yellow lead .. D.C. voltage ↯

Black lead ( L1 ) onto line 1 - U2 .
+ L2 ) other fixed lead onto line 2 - V2 . green light against the ( R► ) on the right side of indicator . that tell you the rotation is correct .

( L1 ) onto L2 - V2 .
+ L2 ) onto L3 - W2 . that tell you the phase rotation is correct .

then the other way around ;

L1 onto L3 - W2
L2 onto L1 - U2 .. that tell you the phase rotation is correct .

if you get it round the wrong way . L1 onto L1 - U2 , + L2 onto L3 - W2 . Left hand green light coming on ( ◄ L ) that tell you the phase rotation is Wrong

 

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TN - system with nominal mains voltage ( Uo = 230V ) Fig 3A4 . BS-EN-60898-1 & BS-EN-61009-1
Protection by circuit breakers with ( Uo of 230V ) disconnection time 0.4 & 5s

( Ia & maximum Zs values could be ) R/P. 301 , 302 , 303 . B , C , D .
Characteristic B . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 30 . Zs ( Ω ) 7.67 .. ( Zs ≤ 230V ÷ 30A = 7.67Ω )
Characteristic C . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 60 . Zs ( Ω ) 3.83 .. ( Zs ≤ 230V ÷ 60A = 3.83Ω )
Characteristic D . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 120 . Zs ( Ω ) 1.92 .. ( Zs ≤ 230V ÷ 120A = 1.92Ω )

Rating / Current

In ) 5 x magnetic settings ; 5 x 6A = 30A
In ) 10 x magnetic settings ; 10 x 6A = 60A
In ) 20 x magnetic settings ; 20 x 6A = 120A

 

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Who sets these questions ?

The usual forum " pick the Answer apart & Criticise "

Q) A ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) reading at the extreme end of a 25m long 20A radial socket-outlet circuit is taken :
What would be the approximate reading of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) given that the résistance per metre of 2.5mm[SUP]2[/SUP] cable is 7.41 mΩ/m at 20ºC .

0.37Ω
0.18Ω
0.74Ω
0.27Ω

• Using Singles.

O.S.G. Table 11 , Temperature is not an issue as 20ºC

( - ) for single cable . ◄

( r[SUP]1[/SUP] + r[SUP]2[/SUP] ) same csa (singles)

Length of cable 25m
Resistance of cable/m ( r[SUP]1[/SUP]) = 7.41 , ( r[SUP]2[/SUP] ) = 7.41

r1 ) - 25m x 7.41 / 1000 = 0.185
r2 ) - 25m x 7.41 / 1000 = 0.185

0.185 + 0.185 = 0.37 The answer .

O.S.G. Table 11 , Temperature is not an issue as 20ºC

• Cable is T&E
Length of cable 25m
Resistance of cable/m

( r1 ) = 7.41............. ( resistance of 2.5mm line-conductor )
( r2 ) = 12.10 ............. ( resistance of 1.5mm circuit-protective-conductor)

r1 ) - 25m x 7.41 / 1000 = 0.185
r2 ) - 25m x 12.1 / 1000 = 0.303

0.185 + 0.303 = 0.488Ω

 

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When selecting equipment the ( designer / Installer ) should take account of manufacturer's instructions (i.e. is this equipment suitable for the purpose (s)

Just back from changing circuit-breakers for RCBOs 20A , Shop work

Manufactures' instruction's on box . ◄

Operation of the test button of any RCBOs fitted

When newly fitted systems do not trip on the TEST button or using the RCBO tester the problem is normally caused by an earth to neutral fault on the circuit ( PME ) supply

Installers can easily check the RCBO by removing the outgoing terminations ( i.e. busbar and neutral link ) on the RCBO and applying power .

if the TEST button works the fault is in the circuit . ◄

Section 134 .. Erection & initial Verification of Electrical Installations .

R/P.21 , 134.1 Erection
Regulation 134.1.1 , Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation, ( Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment. )

Part 5 ; Selection & Erection of Equipment

Chapter 51 , Common Rules
510.3 Every item of equipment shall be selected and erected so as to allow compliance with the regulations stated in this chapter and the relevant regulations in other parts of BS-7671 and ( shall take account of manufacturers' instructions. )

& 511.1. Compliance with Standards .

R/P118 , 514.12.2. Where an installation incorporates an RCD a notice shall be fitted in a prominent position at or near the origin of the installation , The notice shall be in indelible characters not smaller than those illustrated here and shall read as follows : refer

RCD / RCBO .

134 ; is just deals with Erection ( & Verification).

 

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Inspection ..
An action comprising careful scrutiny of an item / system . ( this is the polite way of say it )

Inspection .. R/P.29
Examination of an electrical installation using all the senses as appropriate .

Visual inspection .. which identifies, those defects, which can be apparent to the eye.

 

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( rule of thumb ) ► This type of calculation must be understood by any student studying for the C&Gs 2394 / 5 Inspection & Testing

• Values given in BS-7671:2011: for ( Zs ) are for when the circuit conductors are at their operating temperature , generally 70ºC

On small rant mode .

Comparing Maximum ( Zs ) & Measured ( Zs )

Simple calculation - rule of thumb , Appendix 14 of BS-7671:

This calculation will allow you to compare your measured values with the values in BS-7671:2011:

in these type of calculations you must always use the worst case values to ensure a safe installation .

Circuit-breaker application . circuit protected by a 32A BS-EN-60898-1 type B
your measured value of ( Zs ) is 0.98Ω

By calculation . 5 x 32A = 160 so , 230V ÷ 160A = 1.44Ω
Maximum ( Zs ) at ( 70ºC ) for your circuit is , 1.44Ω

To find the corrected value you must multiply ( 1.44Ω by 0.8 ) ........ 1.44 x 0.8 = 1.15Ω .

1.15Ω now becomes your maximum value & you can compare your measured value directly to it . without having to consider the ambient temperature or the conductor operating temperature .

Your measured value must be less than the corrected maximum value . in this case it is , & the 32A type B device would be safe to use .

 

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( rule of thumb ) ▲▲▲

Unfortunately you cannot compare this value to any measured ( Zs ) value that you have .
• Values given in BS-7671:2011: for ( Zs ) are for when the circuit conductors are at their operating temperature , generally 70ºC

 

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On rant mode .

Just stating the Obvious . C&Gs can ask you any one of these in , Q/As

Gentlemen ; everything you have to known about inspection & testing , is all in GN-3 & BS-7671:2011:

P/396 . Electrical Installation Condition Report .. ( EICR )

Section B reason for producing this Report

Details of the installation . Etc ........
- Occupier : this may not be the owner .
- Estimated age of wiring system in Years
- Evidence of additions / alterations : if Yes , estimate the age in Years
- Installation records available .. regulation 621.1. ???
- Date of last inspection ( date ) That's a good Question . ???

Section D . Extent & Limitation of Inspecting & Testing .

Extent of the electrical installation covered by this report : what does the inspection cover , is it the complete installation or just a part of

Agreed Limitation : including the reasons , Regulation 634.2. are there any areas that are not being inspected , are there circuits which cannot be isolated or tested .

Agreed with : who has the limitations been agreed with .
Operational limitations including the reason : areas not to be entered or access not permitted .

The inspection & testing detailed in this report and accompanying schedules have been carried out in accordance with BS-7671:2008: as amended to ....
What Certificates will be used . Section H , Schedules(s) BS-7671: tell us ; ( EICR ) with Schedule(s) of inspection , & Schedule(s) of test results are attached .

The attached Schedules(s) are part of this document and this report is ( valid ) only when they are attached to it .

it should be noted that cables concealed within trunking and conduit , under floors , in roof spaces , and generally within the fabric of the building or underground , have not been inspected unless specifically agreed between the client and inspector prior to the inspection .

Section E . Summary on the condition of the Installation .
This section is where you would record any concerns which you have about the electrical safety of the installation ,

Extent & Limitation of Inspecting & Testing .. C&Gs
Agreed with : who has the limitations been agreed with . .. C&Gs etc .

Periodic inspection is carried out for many reasons ;
The due date .
Client / customer request
Change of ownership
Change of use .
Insurance purposes .
To inspect the condition of the existing installation , prior to carrying out any alterations or additions .

The frequency of the periodic inspection and any testing which may be required is dependent of the ( type ) of installation , the environment and type of use . BS-7671: What Edition ?? refer to this as the " Construction , Utilization and Environment . and this can be found in Appendix 5 of BS-7671:

 

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C&Gs ( EIC ) what is my main purpose Q/As
□ New installation : ✓
□ Addition : ✓
□ Alteration : ✓

P/390 ( EIC ) Description & Extent of the Installation ; What part of the Installation does this certificate cover :

□ New installation : to be ticked if the whole installation is New .

□ Addition to an existing installation : this box be ticked when the work is added to an existing installation , could be a single new circuit , the installation of circuits in an extension .

□ Alteration to an existing installation : this box is used to indicate that the characterises of the existing installation have been altered . this would include extending / altering a circuit and changing the protective-device . the replacement of consumers unit

Supply Characteristics
1 phase 2 - wire 3 phase 4 - wires ... meaning ( Live conductors ) only

Schedule of Test Results This document is a generic document which can be used with either an ( EIC ) or ( EICR )

 

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[h=4]What are the appropriate testing criteria for a time-delayed RCD whenconnected into a TT system, where the installation was designed prior tothe introduction of the 17th Edition [/h]It would be necessary toverify that the RCD operates within the criteria stated in the relevant productstandard (BS-EN 61008-1) and reproduced in Table 3A ofAppendix 3 - that is between 130 mS & 500 mS

 

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GN-3 , give us a solution for anything . (( Testing is for this reason ))

re-cap ; GN-3 2.7.7.
Insulation résistance testing is a fundamental test for inspectors . do they have to be a reason . !

The purpose of the insulation résistance test is to verify that the insulation of conductors provide adequate insulation , is not damaged and that live-conductors or protective-conductors are not short-circuited .

Insulation résistance test . ( IR )
Neutral / Earth fault can go unnoticed unless an ( IR ) test is carried out , whether the circuit with the Neutral / Earth fault is protected by an RCD or not .

To suit certain situations !!

Regulation 612.3.1. requires that :
Insulation résistance be ( Measured ) between ( live-conductors ) & ( protective-conductor ) connected to the earthing arrangement .

This means that the insulation résistance test must be carried out between the neutral-conductor & Earth ... your reason here is , Any Short should be picked up at this stage .